• A carbon monoxide expert has urged people to watch out for signs of the ‘silent killer’ in their home.

• Carbon monoxide is a colourless, odourless, and tasteless gas that can be deadly. 

• It is known as the ‘silent killer’ because it is incredibly difficult to detect. 

• Various household appliances can give off carbon monoxide.

A carbon monoxide expert has warned people to familiarise themselves with the signs of carbon monoxide poisoning in their home.

Described as the “silent killer”, carbon monoxide is a colourless, odourless and tasteless gas which can be deadly and is incredibly difficult to detect. It is found in various household appliances from gas boilers to wood burning stoves.

Exposure to carbon monoxide gas can starve the body of oxygen causing headaches, dizziness and confusion among other symptoms. In the UK, around 30 people die from carbon monoxide poisoning each year, and about 4,000 people are treated in A&E departments.

High levels of carbon monoxide can kill within minutes while long-term low-level exposure to the toxic gas can have lasting and life-limiting consequences including brain damage and heart problems.

The warning comes as new research by Co-Gas Safety can reveal that more than one-third of people (37%) think low-level exposure is fine to live in. The study also highlighted how almost half of of those surveyed (49%) wrongly believe carbon monoxide alarms can detect any level of the deadly gas, when in fact many are only triggered by higher concentrations in the air.

While two-thirds (65%) of respondents understood their gas boiler posed a risk of leaking CO into their home, two-fifths (40%) admitted they do not get it regularly serviced due to costs. Worse still, nearly a fifth (18%) admitted they were unsure how often their boiler should be serviced.

But, while the majority of those surveyed understood their boiler could potentially leak carbon monoxide gas, far fewer were aware that other everyday household appliances could do the same. Nearly three-quarters (71%) were in the dark about the  threat from their grill while two-thirds had no idea it could come from a wood burning stove (65%) or open fire (66%).

If your carbon monoxide alarm goes off, you should “get out of the property immediately”, however worryingly only just over a quarter (28%) said they would do this. Whilst a third (30%) admitted removing dead batteries from alarms without replacing them. 

Almost one in ten UK homes (8%) was found to be at risk of recording “dangerous levels” of carbon monoxide and nearly half (45%) have received no information about the dangers, highlighting the dangerous lack of awareness about carbon monoxide poisoning.

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What are the symptoms of carbon monoxide poisoning?

President and Director of Carbon Monoxide Gas Safety, Stephanie Trotter OBE said: “You can't see, smell, or taste it – yet in just minutes, carbon monoxide can overwhelm your body's ability to process oxygen. This is why we call it the silent killer. 

Explaining key symptoms to look out for, Stephanie said: “One of the most telling signs of carbon monoxide poisoning is when multiple people in the same building simultaneously develop similar symptoms. If everyone in your household says they feel unwell, have a headache or feel dizzy, it’s unlikely a coincidence - it's a red flag that demands immediate action.”

Other symptoms outlined by the NHS include feeling sick or being sick, feeling weak, confusion, chest and muscle pain and shortness of breath. Symptoms can come and go and may get worse when you’re in a room that is affected.

Stephanie adds: "If you're experiencing symptoms and suspect carbon monoxide exposure, don't wait to see if they improve. Less than 2% concentration of CO in the air can kill in minutes. Get outside immediately and call 999. You are not being overcautious.”

How can you tell if you have carbon monoxide in your house?

Safety experts like Stephanie strongly recommend installing carbon monoxide (CO) alarms that meet BS EN 50291 standards to alert you to the dangers, however, there are other ways of detecting leaks in your home. 

Although carbon monoxide can be hard to detect, there are however a few subtle signs that could have already made their mark on your house. These are the top eight warning signs of carbon monoxide poisoning.

Smell of smoke or burning when using gas or oil appliances 

Although carbon monoxide is odourless, it can reside in other fumes that may be more detectable to smell. When gas or oil appliances begin emitting a smoky or burning odour, it may signal a critical malfunction that could produce this colourless, odourless and sometimes deadly gas.

Despite the warning sign potentially coming from a faulty appliance, proof of carbon monoxide itself is particularly hard to detect without specialized equipment. As an extra safeguard, it is advisable to buy and fit a carbon monoxide alarm to EN 50291 from a reputable supplier. 

Remember to activate the alarm by connecting the battery and regularly test your device to make sure it is working, it should be noted that they are not health monitors and are limited when it comes to detecting low levels of carbon monoxide.

The gas hob burns yellow or orange

If the smell isn’t giving a warning sign on an appliance, maybe the colour is. A yellow or orange flame on a gas hob is a serious safety warning that could indicate dangerous carbon monoxide production. 

Unlike the ideal blue flame, which signifies complete and efficient combustion, yellow or orange flames suggest incomplete burning and potential gas appliance malfunction.

This colour change typically indicates that there is an improper air-to-fuel mixture, potentially caused by blocked burners, dirty components, or misaligned parts. Such conditions can prevent proper oxygen flow, leading to inefficient combustion and toxic gas generation.

Sooty or yellow-brown stains around appliances or chimney

Homeowners should take immediate action if they notice yellow-brown or sooty stains around gas appliances or chimneys, as these marks may signal dangerous carbon monoxide production. 

These discolouration signs often indicate incomplete combustion, which can create toxic gases that pose serious health risks.

These nasty-looking stains typically result from improper fuel burning, potentially caused by blocked ventilation, malfunctioning equipment, or incorrect air-to-fuel ratios. These visual indicators suggest that appliances are not operating efficiently and may be releasing harmful carbon monoxide into living spaces.

Pilot light frequently blows out

A pilot light is a small flame that is kept lit in certain gas-fired appliances, most commonly in appliances like furnaces, water heaters, and gas fireplaces. However, one sign carbon monoxide is present is this light frequently blowing out.

When pilot lights repeatedly go out, it may signal underlying problems with gas appliances that could lead to dangerous gas leaks or incomplete combustion.

These malfunctions often occur due to issues like blocked gas lines, faulty thermocouples, or improper ventilation. These problems can cause gas to accumulate without proper burning, increasing the risk of carbon monoxide production in living spaces.

Residents should avoid reigniting pilot lights repeatedly and contact a qualified technician to diagnose and repair the underlying causes of pilot light instability.

Lots of condensation on the windows

Although condensation on windows can be a very common occurrence due to a wide variety of reasons like the lack of double glazing or ventilation, it can also be a sign of carbon monoxide being present. 

When windows consistently develop heavy condensation, it suggests poor air circulation that can trap toxic gases from malfunctioning fuel-burning appliances.

This moisture build-up may coincide with incomplete combustion in gas appliances, creating an environment where carbon monoxide can accumulate silently.

More than half of those surveyed (56%) have experienced heavy condensation gathering on their windows, showing major issues with the air circulation in British homes, according to the CO-Gas Safety study. The risk of carbon monoxide can be lessened with improvements to home ventilation by installing thicker windows or by investing in a dehumidifier.

Damaged or discoloured bricks at the top of a chimney

Discoloured or damaged bricks at the top of a chimney are more than a cosmetic concern, they may indicate serious carbon monoxide risks. 

Deteriorating chimney bricks can result from excessive heat, moisture, or improper ventilation, potentially creating conditions that prevent proper exhaust of harmful gases. Such damage may allow carbon monoxide to leak into living spaces, posing significant health hazards.

This structural problem will need fixing as soon as possible with the help of a professional chimney inspector, otherwise, the carbon monoxide may be trapped inside your home with no means of escape.

Rusting on flue pipes

High levels of dissolved oxygen can cause your pipes to corrode, which can result in serious ventilation problems that could allow dangerous gases to leak into living spaces.

Rusty pipes can often occur from moisture build-up, poor combustion, or structural damage, potentially compromising the safe exhaust of toxic gases from heating appliances. This deterioration can create conditions that increase carbon monoxide production and exposure risks.

Your pet is acting strangely 

Last but certainly not least, another sign you could have a carbon monoxide leak is the behaviour of your pet. Dogs and cats are often attracted to finding the warmest spots in the house to cosy up in, this unfortunately can lead them to being in frequent close proximity to boilers, which can be a danger zone when emitting carbon monoxide fumes.

For pets, carbon monoxide can interfere with oxygen absorption, causing neurological and physiological distress that manifests through dramatic shifts in animal behaviour and health. Examples of these symptoms can include your cat or dog becoming uncharacteristically aggressive, anxious, fearful or sleepy and can even start vomiting.

If you believe your pet has been exposed to carbon monoxide poisoning get them outside and breathing fresh air immediately and take them to the nearest vet as soon as possible.

You can find out more about carbon monoxide poisoning and how to keep your home safe at The Carbon Monoxide and Gas Safety Society.